The term “HIPE” refers to such an emulsion as has a water phase, namely the dispersed phase (internal phase), and an oil phase, namely the external phase, at a ratio (W/O) of not less than about 3/1. The fact that a porous polymer is produced by the method of polymerizing this HIPE (which will be referred to as “HIPE method” hereinafter) has been known to the art. The porous polymer produced from the HIPE is excellent because it tends to grow into a porous polymer of low density possessed of open cells of a fine diameter, whereas the porous polymer produced by using a foaming agent without being converted into the HIPE tends to grow into a porous polymer possessed of discrete cells of a comparatively large diameter.
The porous polymer is utilized for water absorbent, oil absorbent, sound insulator, filter, and so forth. Whichever of such applications may be chosen, the porous polymer will possibly suffer deficiency in absorbency and filtering efficiency unless it has through holes formed in the surface and in the interior thereof. In the production of the porous polymer from the HIPE, however, the so-called skin layer will be possibly formed in the interface of contact between the polymerization vessel and the HIPE owing to the action of the quality of material of such a device as the polymerization vessel which is exposed to the HIPE. This skin layer is known to degrade the numerical aperture of the porous polymer and exert adverse effects on the liquid permeability, filtering property, and absorbency of the porous polymer. When the skin layer is formed on the surface of the porous polymer, the entire surface layer of the porous polymer may be wholly sliced and discarded. When this measure is adopted, however, the slicing will remove part of the internal texture of the porous material and entail a dramatic reduction in the yield of product.
It is, therefore, an object of this invention to provide a method for the production of a porous polymer by the polymerization of the HIPE which is free from such conventional technical problems as mentioned above and more particularly to provide a method for producing highly efficiently a porous polymer having a small difference in texture between the interior and the surface of the porous polymer to be produced and possessing excellent characteristic properties (such as, for example, the liquid passing property and the absorbency of the porous polymer) with high degree of freedom of selection regarding the composition of the HIPE, the apparatus of polymerization, and the conditions for polymerization.